(i) Field of the Invention
The present invention relates to a waste water treatment device for waste water containing phosphoric acid, phosphorus compounds, phosphate ions, organic nitrogen, nitrite nitrogen, nitrate nitrogen, nitrate ions, and ammonia.
(ii) Description of the Related Art
It is well known that the presence of phosphorus compounds and nitrogen compounds is one of the causes of nutrition richness of a river or lake. Besides, many phosphorus compounds and nitrogen compounds exist in waste water from homes, but a purification treatment of these compounds is difficult and no effective measure exists.
Various treatment devices for phosphorus compounds have been proposed, but as for waste water from homes, an electrolytic dissolution method of iron is known (Japanese Patent Application Laid-open No. 3-89998). This technique is a technique in which phosphate ions in waste water are reacted with iron ions, and condensed and precipitated to be removed as water-insoluble salts such as FePO4 and Fe(OH)x(PO4)y, and an iron electrode disposed in an electrolytic bath is electrified to dissolve out iron ions. Furthermore, as a waste treatment device using such an electrochemical elution method of iron, for example, there is a device that comprises an anaerobic bath, an aerobic bath, and a treatment water bath. In this kind of device, waste water in the treatment water bath is circulated through the anaerobic bath via the treatment bath in which iron ions to react with phosphoric acid ions are dissolved out.
In the anaerobic bath, denitrifying bacteria live that exist only in this anaerobic bath, and therefore, nitrate ions and nitrite ions in circulated waste water are reduced into nitrogen gas, thereby removing nitrogen from the waste water. However, in the denitrifying reaction by the above-mentioned denitrifying bacteria, reaction time is long, and hence, there is a problem of decreased treatment efficiency. In addition, to keep sufficient denitrifying bacteria, an anaerobic bath having a large volume is required, and so there are problems of an increase in equipment cost and an increase in an equipment disposition area. Further, since the denitrifying bacteria deteriorate in action especially in winter, there are problems that the denitrifying action deteriorates and the treatment efficiency becomes instable.
Therefore, to solve the above-described technical problems, as shown in FIG. 2, there is a contact reduction treatment in which hydrogen is fed from a hydrogen cylinder (not shown) into the anaerobic bath 100 via a gas scattering plate 101, and a reducting catalyst 102 is used as a catalyst in the presence of the H2 gas. On the basis of this treatment, a method in which the denitrifying treatment is performed stably and efficiently has been provided. In addition, a method of using a metallic reaction of zinc or the like in an alkali solution has also be provided.
In the above various denitrifying treatments, however, there are problems that the device is complicated and an increase in cost exists. Moreover, there is also a method of adding a necessary agent for pH control, but the method has a problem of maintenance.
Accordingly, the present invention has been developed in order to solve the conventional technical problems, and an object of the present invention is to provide a waste water treatment device in which removal of phosphorus and removal of nitrogen can efficiently be carried out and a decrease in the size of the device and a decrease in cost can be achieved.
A waste water treatment device of the present invention is characterized by comprising a waste water treatment chamber; at least one set of electrodes disposed so that at least part is immersed in waste water in the waste water treatment chamber, at least one of which dissolves out by electrolysis iron ions or aluminum ions for precipitating and removing phosphoric acid ions in waste water; a power source for supplying an electrolytic current to the set of electrodes; a control section for controlling the power source; and a metallic catalyst disposed in the vicinity of at least one electrode of the set of electrodes effect on the denitrifying reaction with hydrogen generated from the electrode in waste water.
According to the present invention, there are provided a waste water treatment chamber; at least one set of electrodes disposed so that at least a part of the electrodes are immersed in waste water in the waste water treatment chamber, at least one of the above electrodes dissolving out, by electrolysis, iron ions or aluminum ions for precipitating and removing phosphoric acid ions in waste water; a power source for supplying an electrolytic current to the set of electrodes; a control section for controlling the power source; and a metallic catalyst which is disposed in the vicinity of at least the other of the set of electrodes and which effects a denitrifying reaction with hydrogen in waste water. Therefore, on the electrode side on which iron ions or aluminum ions are dissolved out by electrolysis, precipitation and removal of phosphoric acid ions can be performed, and on the other electrode side, removal of nitrogen can be performed by the metallic catalyst that effects the denitrifying reaction by hydrogen generated from the electrode, and therefore the removal of phosphorus and the removal of nitrogen can be performed together.
Since the waste water treatment device according to the present invention is constituted by a waste water accommodation chamber, at least one set of electrodes, the control section, and the metallic catalyst, the device becomes simple and a decrease in size of device and a decrease in cost result. Further, in the waste water treatment device according to the present invention, since any biological catalyst, which is used for a denitrifying reaction, and any chemical for controlling pH in the waste water accommodation bath, as conventional, are not used, the treatment of waste water can be performed without being affected by the environment in which the waste water treatment is performed.
In comparison with the conventional waste water treatment device, the amount of mud generated after treatment can remarkably be decreased.
In addition to the above invention, the waste water treatment device of the present invention is characterized in that both of the sets of electrodes are used as electrodes for dissolving out by electrolysis iron ions or aluminum ions for precipitating and removing phosphoric acid ions in waste water, the metallic catalyst is disposed in the vicinity of each electrode, and by periodically reversing the polarities of the electrodes by the control section, removal of phosphoric acid ions by iron ions or aluminum ions is performed on the electrode side whose polarity is anode, and removal of nitrogen by a denitrifying reaction by hydrogen generated from the electrode is performed under the metallic catalyst on the electrode side whose polarity is cathode.
In another embodiment, both of the set of electrodes are used as electrodes for dissolving out, by electrolysis, iron ions or aluminum ions for precipitating and removing phosphoric acid ions in waste water; the metallic catalyst is disposed in the vicinity of each electrode; and the polarities of the electrodes are periodically reversed by the control section to carry out the removal of phosphoric acid ions by iron ions or aluminum ions on the side of the electrode whose polarity is anode and to carry out the removal of nitrogen by a denitrifying reaction with hydrogen generated from the electrode in the presence of the metallic catalyst on the side of the electrode whose polarity is cathode. Since the electrodes are periodically reversed in polarity, the inconvenience that only one electrode is dissolved out and the electrode is used up or inactivated can be avoided.
A waste water treatment method of the present invention is characterized by comprising at least one set of electrodes disposed in a waste water treatment chamber so that at least part is immersed in waste water, at least one of which dissolves out by electrolysis iron ions or aluminum ions for precipitating and removing phosphoric acid ions in waste water; a control section for supplying an electrolytic current to the set of electrodes and controlling the electrolytic current; and a metallic catalyst disposed in the vicinity of at least the other of the set of electrodes to effect the denitrifying reaction by hydrogen generated from the electrode in waste water.
According to this invention, at least one set of electrodes is disposed in a waste water treatment chamber so that at least a part of the electrodes are immersed in waste water, at least one of the electrodes dissolving out, by electrolysis, iron ions or aluminum ions for precipitating and removing phosphoric acid ions in waste water; a control section is disposed for supplying an electrolytic current to the set of electrodes and for controlling the electrolytic current; and a metallic catalyst is disposed which is provided in the vicinity of at least one of the sets of electrodes and which effects a denitrifying reaction with hydrogen generated from the electrode in waste water. Therefore, on the side of the electrode on which iron ions or aluminum ions are dissolved out by electrolysis, precipitation and removal of phosphoric acid ions can be performed, and on the other electrode side, removal of nitrogen can be performed by the metallic catalyst that effects the denitrifying reaction by hydrogen generated from the electrode, and so the removal of phosphorus and the removal of nitrogen can be performed together.
In the waste water treatment method according to this invention, since any biological catalyst, which is used for a denitrifying reaction, and any chemical for controlling pH in the waste water accommodation bath, as conventional, are not used, the treatment of waste water can be performed without being affected by the environment in which the waste water treatment is performed.
In comparison with the conventional waste water treatment method, the amount of mud generated after treatment can remarkably be decreased.
In each embodiment described above, the present invention is characterized in that the electrodes are made of a noble metal modified with copper atoms, or copper.
According to this invention, in addition to each invention described above, since the metallic catalyst is made of a noble metal modified with copper atoms or copper, on the electrode side at which iron ions or aluminum ions are dissolved out by electrolysis, precipitation and removal of phosphoric acid ions can be performed, and on the other electrode side, the removal efficiency of nitrogen can be improved when removal of nitrogen is performed by the metallic catalyst that effects the denitrifying reaction by hydrogen generated from the electrode.
Still further, in addition to each invention described above, the present invention is characterized in that a diaphragm is provided between the electrodes.
According to this invention, in addition to each invention described above, since the diaphragm is provided between the electrodes, the removal efficiency of nitrogen by the denitrifying reaction can be improved further.